In recent years, Mobile IP and Mobile IPv6 are being examined as schemes for providing a mobile terminal device with mobility on an IP network (For example, Non-Patent Document 1). Hereinafter, description will be made using a mobility control technique in an IPv6 network for simplicity, and Mobile IPv6 is referred to as Mobile IP.
In Mobile IP, a device implementing Mobile IP (an MIP terminal) uses two types of IP addresses so that communication continuity is achieved. That is, the MIP terminal uses Home Address (hereinafter abbreviated as HoA) and Care-of Address (hereinafter abbreviated as CoA). The HoA is an address which is used by a terminal application and assigned on a home link. On the other hand, the CoA is an address which is dynamically acquired by a Router Advertisement (RA) that is advertised from a connected access router on an external link to the MIP terminal or a Dynamic Host Configuration Protocol (hereinafter abbreviated as DHCP) and used for packet forwarding.
In addition, on the home link, a Home Agent (hereinafter abbreviated as HA) which manages combination information of HoA and CoA is placed for managing mobility information of the MIP terminal. The MIP terminal sends a Binding Update signal on periodical basis as well as when the CoA is updated to register combination information of HoA and CoA with the HA.
In addition, the HA has a function to forward a packet addressed to an MIP terminal whose address is HoA to the terminal by encapsulating the packet using CoA information registered with the HA. This allows a packet to be constantly forwarded to a current location of the MIP terminal, even if CoA is dynamically changed due to movement of the terminal, by registering the change with the HA through transmission of the Binding Update, so that a communication system which provides communication mobility can be constructed.
However, in mobile IP, each time the terminal moves across access routers (hereinafter, access router is abbreviated as AR), it is required that the CoA is updated and a Binding Update signal is sent to the HA installed in a home network to update combination information of HoA and CoA. Therefore, there is a problem that the terminal cannot receive a packet in a time in which the update of the CoA and the transmission of the Binding Update signal are completed, and thereby a service of a terminal application is interrupted (hereinafter, this problem is referred to as the problem A).
There are proposed some schemes for reducing such a service interruption time to provide seamless mobility to a terminal which performs real-time application. Among them, as protocols in which prediction of movement of a terminal is not assumed, there are Hierarchical Mobile IPv6 (HMIP) (for example, see Non-Patent Document 2) and unplanned handover of Brain Candidate Mobility Management Protocol (BCMP) (for example, see, Non-Patent Document 3). These will be hereinafter described.
(HMIP)
FIG. 21 is a schematic diagram which shows an operation example of HMIP. In HMIP, Mobility Anchor Point (MAP) is introduced which has a function equivalent to HA as a node which controls mobility.
An MAP 31 is located in a position at which ARs 11 and 12 are bound, and manages mobility information of a terminal 10 which moves between the ARs under the MAP 31. An MAP 32 is also located in a position at which an AR 13 and so on are bound and manages mobility information as well.
In HMIP, two types of CoA, i.e., Local CoA (hereinafter abbreviated as LCoA) which is updated each time an AR is moved, and Regional CoA (hereinafter abbreviated as RCoA) which is updated each time an AR is moved across an area corresponding to an MAP and provides a function equivalent to CoA in mobile IP, are defined. Then, RCoA is registered with the HA, and combination of RCoA and LCoA is registered as mobility information with the MAP. Thereby, a packet which is sent from a CN (Correspondent Node) that is a communication partner to the terminal is forwarded via the HA (not shown) to the MAP, and further forwarded to the terminal referring to the mobility information of the MAP.
Then, if the mobile terminal device 10 moves between the ARs under the MAP (step S1), an LCoA is generated using advertisement information received from the destination AR 12 (step S2), and a combination of the updated LCoA and the RCoA which is the same as before the movement is just registered with the MAP (step S3), but the RCoA is not updated and registered with the HA.
On the other hand, if the mobile terminal device 10 moves across MAPs (step S4), an LCoA and an RCoA are generated using advertisement information received from the destination AR 13 (step S5), and an MAP information table which holds an IP address of the MAP managed by the terminal itself is updated (step S6). Then, the mobile terminal device 10 notifies the HA of the updated RCoA by a Binding Update (not shown), and notifies the MAP of the updated RCoA and LCoA by a Local Binding Update (step S8). In addition, for reducing packet loss during handover processing, a request notification may be made for an MAP that was connected at a previous time (hereinafter referred to as old MAP) so as to forward a packet arrived at the old MAP to the updated LCoA in a time until the Binding Update to the HA is completed (step S7). Thereby, the mobility information is updated.
As described above, with respect to movement under an MAP, a time until completion of a transmission of Binding Update, which is one of the causes of service interruption in a conventional MIP, is reduced by registering terminal position information with an MAP that is closer to the terminal than the HA. By processing in this way, a time required for handover is reduced and reduction of service interruption time in a terminal application is achieved.
As described above, to realize the HMIP, an IP address of an MAP which manages movement between ARs is added to an RA which is sent from an AR on periodical basis or upon request of a terminal, so that the terminal is notified of the IP address. The terminal creates an RCoA from the IP address of the MAP contained in the RA, and an LCoA by Prefix information of the AR contained in the RA or DHCP. Acquired MAP information is held by the terminal constantly and used for sending Local Binding Update to the MAP. In addition, if the terminal moves across MAPs, with respect to the old MAP held by the terminal, new LCoA information acquired at an MAP to which the terminal moves (hereinafter referred to as new MAP) is sent to an old MAP.
Therefore, although a packet is forwarded to an old RCoA while a new RCoA is registered with the HA, the new LCoA that is a forwarding address is registered as mobility control information with the old MAP, so that the terminal can receive this information under a destination AR and thus packet loss is reduced.
(BCMP)
FIG. 22 is a schematic diagram which shows an operation example of BCMP. As BCMP, there are a handover control scheme using movement prediction (planned handover) and a handover control not using movement prediction or for prediction failure (unplanned handover). FIG. 22 illustrates an operation example of BCMP in the latter case.
BCMP is constructed by a BRAIN Access Router (BAR), an Anchor Router (ANR), and other routers which implement BCMP. In FIG. 22, operation of a terminal in communication for moving across BARs in an ANR 4 is noted for simplicity, so that only operations associated with the BARs 51 and 52 and the ANR 4 are shown. Additionally, it is assumed that an IP address is assigned to the mobile terminal device 10 from the ANR when the mobile terminal device performs a connection process to connect to the network, and a tunnel control process required for encapsulated forwarding is performed between the ANR and BAR in advance. Therefore, a packet sent from its communication partner to the IP address of the terminal is forwarded to the ANR 4, and then forwarded to the BAR 51 to which the terminal currently connects based on the tunnel control information determined by the IP address of the mobile terminal device 10.
In the figure, when the terminal moves from the currently connected BAR (hereinafter referred to as old BAR) 51 to the destination BAR (hereinafter referred to as new BAR) (step S11), the terminal obtains information of the new BAR 52 (step S12), and then sends a handover request signal containing information of the old BAR to the new BAR 52 (step S13). The new BAR 52 sends a handover start request signal to the old BAR 51 based on the old BAR information based on the received signal (step S14). When the old BAR 51 receives this signal, a packet addressed to the IP address of the mobile terminal device 10, which is to be encapsulated and sent from the ANR 4 to the old BAR 51, is addressed to the new BAR 52 and forwarded by encapsulating the packet (step S15, S16).
By the means as described above, the new BAR 52 sends a redirect signal to the ANR 4 (step S17), and the mobile terminal device 10 can receive the packet which arrives at the old BAR 51 from the ANR 4 while tunnel control information between ANR and BAR stored in the ANR 4 is rewritten. Consequently, packet loss can be reduced.
As described above, in BCMP, a terminal notifies a new BAR of old BAR information, and thereby the above described handover control is achieved.    Non-Patent Document 1: “Mobility Support in IPv 6”, RFC3775, June, 2004    Non-Patent Document 2: “Hierarchical Mobile IPv6 mobility management (HMIPv6)”, draft-ietf-mipshop-hmipv6-04.txt, December, 2004    Non-Patent Document 3: Keszei, C., Georganopoulos, N., Turuanyi, Z. and A. Valko, “Evaluation of the BRAIN Candidate Mobility Management Protocol”, IST Summit Barcelona, September 2001.
However, the HMIP and BCMP described above have problems as described below.
In the HMIP and BCMP described above, to solve the problem A described above, the terminal needs to know an address of a control node (an MAP in HMIP, a BAR in BCMP) to which the terminal provides a mobility service, and the terminal itself needs to perform mobility processing directly or indirectly on the control node. Because of this, notification of an address of the mobility control node in a network must be given to the terminal in advance or in any way, and thus there is a problem that a network operator cannot hide information of a mobility control node whose existence is desired to be hidden from the outside of the network with respect to security.
Additionally, in HMIP or the like, since a function of HMIP is required to be added to a terminal side to overcome a problem of MIP, advance mobility control cannot be transparently provided to a terminal which has only a function of a conventional mobility control scheme such as MIP.
To solve the foregoing problems, it is contemplated that, in a network which accommodates a mobile terminal, an address of a service providing device is uniquely determined on the network side without notifying the terminal of the address of the service providing device which provides a service to the terminal and without requesting the terminal side to add a function to the terminal side. The present invention is made to solve the above described problems of the prior arts, and the object of the present invention is to provide an access router, a service control system, and a service control method which allow a network to transparently provide a service to a mobile terminal device without the mobile terminal device knowing an address of a service providing device or a device which relays a packet in a network.